The invention concerns a vibration damper for a hydraulic motor vehicle brake installation with a membrane facing the hydraulic medium transferring the braking force which is finally fastened with its edge region on a carrier element functioning especially as a brake piston in the brake saddle of a motor vehicle brake which can move with its central region at least slightly toward the carrier element or away from this. Regarding the state of the art, reference is made to German Patent Document DE 195 44 223 A1 and to the not previously published German Patent Application DE 100 05 588.5.
It can be necessary to provide a vibration damper for a hydraulic motor vehicle brake installation with a membrane facing a hydraulic medium transferring a braking force, the membrane being fastened via an edge region to a carrier element functioning as a brake piston in a brake saddle of a motor vehicle, and the membrane being movable at least slightly toward the carrier element or away from the carrier element in a central region in a hydraulic brake installation in order to diminish undesired vibrations in the hydraulic system in this way, or to prevent small vibrations caused by any disturbing forces whatsoever from amplifying to a no longer tolerable intensity. Here a vibration damper of this type can also be designated as a xe2x80x9cpressure smoother.xe2x80x9d For this purpose, spring-stressed vibration dampers, for example, can be used, but they are relatively expensive. A vibration damper known on the basis of the aforementioned German Patent Document DE 195 44 223 A1 and corresponding U.S. Pat. No. 5,730,506 is basically simpler, having a housing or a carrier element with a concavely constructed recess closed off by a disk-like membrane of spring plate. This membrane, which is subject to stress externally from the hydraulic medium of the brake installation, is welded on its edge side with the carrier element, and the hollow space between the membrane and the recess mentioned is filled with air. Pressure fluctuations arising in the hydraulic system occasion the membrane to move into the hollow space with its center region and away from the carrier element again, through which, with a suitable design, a vibration damping can be attained.
In order to prevent air from getting out of the hollow space between membrane and carrier element into the hydraulic system when the necessarily relatively thin and consequently weakly constructed membrane tears, it is proposed in the not previously published patent application DE 100 05 588.5 that the hollow space necessary for the membrane motion be evacuated to the greatest extent between the membrane and the carrier element.
It should now be pointed out with the present invention how a vibration damper of the above-mentioned kind can be more simply finished or manufactured, which is an object of the present invention.
The solution of this objective is characterized in that the membrane forms a membrane unit together with a further membrane whereby the two membranes arranged basically one over the other are fastened to each other in their annular edge section and thus lie tightly upon each other and enclose a hollow space between themselves in the central region within this edge section. Advantageous constructions and refinements are in the preferred embodiments.
While in the known state of the art the vibration damping takes place by means of a single membrane which is moved relative to a so-called carrier element where it is a matter of the brake piston of a brake saddle of the motor vehicle brake, and whereby the volume of a hollow space enclosed between this carrier element as well as the membrane is altered when the pressure prevailing in the hydraulic medium changes, a so-called membrane unit is provided according to the invention which consists of two membranes between which the aforementioned hollow space is situated whose volume is changed owing to pressure fluctuations in the hydraulic medium lying outside on at least one of the membranes.
With the known state of the art, the membrane must be joined tightly externally with the carrier element in order to create the hermetically sealed off hollow space for a successful vibration damping of pressure smoothing. With the present invention, the fastening of the membrane unit on the carrier element can basically be more simply configured. For example, with the known state of the art, the membranes are welded with the carrier element in their edge region, which is relatively expensive owing to the requisite tightness. However, according to the present invention, the membrane unit can simply be held in a suitable groove or the like in the carrier element. Of course, in this connection it is necessary to join the two membranes of the membrane unit tightly and firmly with each other in their annular edge section, for example likewise by welding, but this connection between two membranes lying on each other can be completed distinctly more simply than such a connection between a thin membrane and the carrier element/brake piston, which is plainly more massive by comparison.
It was already mentioned that the membrane unit can be fastened simply in a groove or the like provided in the carrier element, especially at the edge of a recess, namely by pressing in or insertion, but for example also in the manner of a bayonet lock. Preferably, this connection between membrane unit and carrier element or brake piston can here be constructed in such a way that the membrane facing the carrier element or its surface is set at a distance apart from the so-called fastening section of the membrane unit on the carrier element, and that the space between the surface of the carrier element and the membrane facing this and thereby set at a distance from this stands in fluid contact with the hydraulic medium. Then the membrane unit is namely acted upon from both sides, that is, on the outside of the two membranes forming this unit with the pressure fluctuations in the hydraulic medium, so that the entire surface of the membrane or the membrane bringing about the desired vibration damping is considerably enlarged, almost doubled, with unchanged dimensioning of the carrier element/brake piston. With pressure fluctuations in the hydraulic system, the two membranes of the membrane unit are consequently deformed.
In order to achieve a certain damping action, the material thickness of the membrane can be almost doubled with the measure just described in comparison with a membrane acted upon only on one side according to the known state of the art, which is extremely conducive to the durability of this vibration damping system. Nonetheless, evacuating the hollow space between the membranes as far as possible can be worth recommending even with a membrane unit of the invention in order to avoid the entry of air into the hydraulic medium in the event of a membrane tear or rupture.
The effective surface with respect to the desired effect, namely vibration damping, can be even further enlarged with specified dimensions of the carrier element, and the damping action can be once more enlarged if the membranes are constructed corrugated or wave-like at least area-wise. This wave shape can here be provided on the two membranes synchronously or a synchronously toward each other. In particular for reasons of toughness, selecting the geometrical dimensions such that, in the basically unstressed state of the membrane unit, that is, when no braking pressure is introduced into the hydraulic medium, the distance between the two membranes forming the center of the central region is greater near the already mentioned so-called edge ring, on which the two membranes lying on each other are fastened to each other, can furthermore be worth recommending.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.